This invention relates generally to an improved system for the vaccum unloading and transferring of dry, bulk, particulate material from a container such as a vessel, a river barge, an ocean-going ship or the like. Systems utilizing a basic vacuum technique to transfer dry, bulk, particulate material are, of course, well-known as described in U.S. Pat. No. 3,373,883 assigned to the assignee of the present invention and entitled "Barge Unloading System".
In the unloading of dry, bulk, particulate material such as cement powder, grain or fertilizer, it is known that the material is fluidized when mixed with a transport medium such as air and thus the material may be conveyed and transported as if it were a fluid material. The actual conveying or transporting of the fluidized particulate material is accomplished by a nozzle connected ultimately to a vacuum pump, to provide suction or negative pressure, as is conventional.
There are, of course, well known vacuum unloading systems. In one such system, described in U.S. Pat. No. 3,373,883, there are two pressure vessels or containers which are alternately filled from the barge. As one vessel is being filled, by suction or negative pressure, the other vessel is being emptied, by a positive pressure or blower, into a permanent storage vessel such as a silo. The equipment used for the system of U.S. Pat. No. 3,373,883 is quite expensive since it requires two complete pressure vessels into which the dry, bulk, particulate materal is initially transferred by vacuum.
To overcome the expense of two pressure vessels, systems have been developed which utilize a singe nozzle system, a single pressure vessel, and the use of constant vacuum or negative pressure to fill the pressure vessel. An exemplification of such a system is found in U.S. Pat. No. 3,489,464, in which system the particulate material itself is utilized to establish a seal between the negative pressure or vacuum at the inlet side of the pressure vessel and the ambient pressure at the outlet side of the pressure vessel. These types of systems require that the level of material in the pressure vessel be maintained substantially constant to provide sufficient material in the pressure vessel to maintain the sealing effect between the negative pressure inside the vessel and the ambient pressure outside the vessel. Hence several types of problems may arise. First, an excessively large discharge of material from the pressure vessel may break the seal between negative pressure and ambient pressure. Second, where there is no more particulate material in the ship or barge, as the pressure vessel is discharged the height of material in the pressure vessel will be insufficient to maintain the seal. Third, the rate of discharge of material from the pressure vessel will not be constant, thus there will be a non-optimum, inefficient use of the conveying means which transfers the particulate material from the pressure vessel to a storage silo.
Yet another technique for particulate transfer according to the prior art is exemplified by Swiss Pat. No. 376,430 which shows upper and lower containers for an unloading apparatus. The Swiss patent does not disclose how the particulate material is initially introduced into the upper container. The material is transferred from the upper container to a lower container apparently under the influence of gravity and, thereafter, air is introduced into the lower container to pressurize the lower container and thus force the particulate material out of the lower container.
The present invention overcomes the problems of the prior art by providing a new and improved method and apparatus for unloading dry, bulk, particulate material using only a single nozzle system and a single pressure vessel, without the problem of maintaining a seal between the pressure vessel and the ambient air, and without the need for positive pressure to transfer material from the system to a silo or permanent storage device.